The invention concerns electric generators of heat.
There are countless processes and types of apparatus for generating heat all based essentially on the combustion of gas, fuel oil and coal, and on electric resistances.
The thermal chain so set up conditions the thermal efficiency of these heating systems.
Heat may be produced in a boiler or oven and is transferred from there, by means of a diathermic liquid such as water or oil, to a central heating plant that supplies warmth to indoor areas or rooms, or to the bodies to be heated by conduction or convention.
In the first case the heater must be placed in contact with the body to be heated.
In the second case heat from the hotter body is passed into the environment or to the body to be heated by some fluid. such as air for example.
The heating device must have a large surface area to enable great quantities of heat to be emitted at a low thermal head in order to avoid overheating the walls of the device which would damage the fluid circulating inside.
The diathermic liquids must posses certain characteristics, above all that of maintaining stability at a high temperature.
For temperatures up to 310-350xc2x0 C. mineral oils are often used today in the form of high-boiling fractions of oil refined to remove unsaturated substances that might become polymerized, while special additives are put in to improve thermal stability so interrupting chain reactions and cracking.
The mode of radiancy transfers heat from the hot body to the colder body by means of electromagnetic waves.
This mode is usually realized by electric heating elements that transform electric energy into thermal energy.
To assist radiancy metal reflectors are used to diffuse heat rays but efficiency is generally lower than diffusion by other methods as the electric elements reach very high temperatures and heat the air closest to them so setting up a convective movement.
With the methods described it will be clear that there is considerable loss of heat along the thermal chain, especially on account of the great differences in temperature between the flame or electric heating elements and that of the body to be heated, the actual quantity of energy used, compared with that available, therefore being very low.
Generation of heat by radiancy through emission of electromagnetic waves creates a risk of deflagration especially in installations where inflammable substances in the gaseous or aeriform state are present.
From the foregoing it will be seen that present methods of creating radiancy are expensive, low in efficiency and possibly dangerous. The above invention permits heat* to be generated achieving a much higher level of efficiency than that possible with other methods, eliminating all danger and offering other considerable advantages as will be explained below.
*The prior patent U.S. Pat. No. 5,804,791 describes a heating structure to be placed in a sandwich-type apparatus, comprising a nichel-chrome or constantan electric resistance substantially embedded in a body of thermoplastic resins, inserted between two rigid elements at least one of which acts as a heating plate. 
When applied to a flat iron, the vaporizing chamber is rendered hermetic, in relation to said heating structure, by silicon joints.
It will be clear that such joints cannot adequately withstand high mechanical and thermal stresses and this would make it impossible to use a heating structure of the kind in environments, or in appliances where inflammable substances or gases are present, due to serious risks of causing a deflagration.
Subject of the invention is a heating device having an electric resistance placed inside a hermetically sealed structure of the sandwich-type, comprising two rigid elements one of which acts as a heating plate.
The electric resistance takes the form of a serpentine and consists of a highly conductive strip of thin material of constant width, the ratio between width and thickness being substantially 10 to 20, that forms a number of U-shaped bends, passed through by a series of parallel and transversal strips of mica.
The serpentine lies between two sheets of mica inside the chamber of a rectangular substantially box-shaped panel, the basic structure being that of a tray having one or more tray-like closing structures inserted side by side inside said basic structure.
The external length of said closing structures corresponds to the internal length of the basic structure less the width of a rectangular supporting plate connecting, by means of hermetically sealed bushes, to the electric feed wiring of the serpentine.
The overall external width of said closing structures laid side by side corresponds to the internal width of said basic structure, while the external height of each of said closing structures corresponds to the internal height of said basic structure less the overall thickness of the serpentine, of the sheets and of the transversal strips of mica.
Said basic structure and each of said closing structures are each formed of a rectangular metal sheet bent at 90xc2x0 at the four sides and joined at the corners by continuous welding.
Continuous welding is carried out on all edges of the basic and closing structures and on the upper face of said rectangular plate matching and practically lying on one and the same geometrical plane.
The effect of all this is to ensure that the chamber of the panel is hermetically sealed and that its free volume is insufficient to receive a quantity of inflammable gaseous substances such as could provoke a deflagration.
The first transversal strip of mica at the bends in the serpentine passes under the first and over the second element of each successive bend as far as the opposite side of said serpentine.
The second strip passes, at a short distance from the first, over the first and under the second element of each successive bend until it reaches the opposite side of the serpentine.
The third and fourth strips follow paths respectively similar to those of the first and second strips, and so on to complete the serpentine. The serpentine can advantageously be made of copper or brass.
Thickness and width of the serpentine are advantagously of about 0.5 mm and 7 mm respectively.
A continuous vertical oven for polymerization comprising the devices for heating by panels and electric resistances as described, presents a vertical structure, two parallel chambers placed side by side consisting of a series of panels aligned on parallel opposing geometrical planes, inside which an impregnated band passes, said band unwinding from a reel at the entry to the oven and, after polymerization, winding onto a reel at the exit from the oven.
A continuous horizontal oven for polymerization, comprising the devices for heating as described, presents a chamber formed of a parallel opposing pair of two sets of aligned panels, inside which an impregnated band passes, said band unwinding from a reel at the entry to the oven and, after polymerization, winding onto a reel at the exit from the oven.
A continuous horizontal oven for polymerizing sheets of copper or other material treated with paints, inks and the like, comprising the heating devices described above, presents a chamber formed of a parallel opposing pair of two sets of aligned panels, and a continuous chain fitted with pincers which, by suitable automatic means, pick up the sheets one at a time from a bed at the entry to the oven and carry them inside said chamber.
In another execution said oven presents a chamber, formed of a parallel opposing pair of two sets of aligned panels, inside which passes a bend of a continuous conveyor belt supported at the two ends, where it enters and leaves the oven, by two rollers one motor driven, enabling said sheets to be deposited one after another on said belt.
A static oven comprising the heating devices as described presents the panels applied to all or some of the walls of said oven, such walls also including the roof and the floor.
A bath for heating, comprising the heating devices as described, presents the panels applied to all or some of its internal walls, such walls also including the roof and the bottom.
A tank for heating, comprising the heating devices described, presents the panels applied to all or some of its internal walls, such walls also comprising the bottom.
A hotplate, comprising the heating devices as described, presents the panels applied to the surface of the hotplate to be used for heating or cooking various substances.
A generator of heat for rooms in buildings generally, comprising the heating devices as described, is formed from one or more units of said panels.
The invention offers evident advantages.
By placing the serpentine, that transforms electrical energy into thermal energy, inside a hermetically sealed metal chamber, of a size substantially the same as that of said serpentine with its sheets of mica, and creating said hermetic seal by continuous welds along all the matching edges of the parts forming said chamber, the described panels can also be used in installations and in places where the risk of deflagration exists due to the presence of inflammable gaseous substances.
Heat is generated by electric current already diffused and therefore at the temperature required for carrying out the processes without any need for diffusers, providing a much higher level of efficiency compared with that obtainable with materials well known to be classified as resistive.
In this latter type of material the electrones strongly resist separation from the core this being the effect of passage of electric current.
In highly conductive materials such as copper, brass and the like used in this present patent application, the electrones offer far less resistance to separation from the core such as is caused by passage of electric current.
As emission of heat is linked to the path taken by the electrones, it follows that transformation of electric energy into thermal energy using highly conductive materials of suitable dimensions, takes place at a considerably higher level of efficiency than that achievable with ordinary resistive materials.
From the above it will be seen that subject panels present two basic characteristics:
a degree of efficiency much greater than that of ordinary generators of heat for transformation of electric energy;
complete safety from deflagration making them usable in practically any installation and in any environment.
The fact of obtaining a method of high-efficiency heating by electricity, one that is free from risk, even in places where deflagration may occur, means that the invention here described can be used with all the advantages pertaining to electric heating, namely maximum possibility of adjustment, easy installation, very low bulk and weight compared with other forms of heating.
The above also shows that these panels provide an interesting application in impregnating systems, in ovens for drying and for polymerizing paints and inks as well as in a wide range of installations and equipment.
Particularly in the fields of impregnating means for polymerization of bands for printed circuits, great importance is attached to the drastic reduction in waste, as seen in FIGS. 5 and 6 respectively relating to radiographic pictures of bands made either with the usual method of heating or with heating by the panels subject of the invention.